Method of manufacturing bimetallic high-speed cutting tools

ABSTRACT

A bimetallic high-speed cutting tool having a series of spaced teeth provided on one of its longitudinal edges is manufactured by providing each tooth at its forward top end with a cut-out portion on which a tip of super-hard material, molded before being sintered into a shape substantially equal to a desired final configuration, and having as cutting edges sharp square corners, is welded or brazed, so that the machining of said tip to said desired final configuration, after it has been welded or brazed to the tooth body is minimized, the super-hard materials constituting said tip being selected from those having such hardness and flexural strength as not to be affected by the heat applied thereto when the tip is welded or brazed firmly onto the tooth body.

United States Patent Funakubo Apr. 2, 1974 2,318,549 5/1943 Wilkie 29/95B Primary Examiner-Lconidas Vlachos Attorney, Agent, or FirmShlesinger,Fitzsimmons &

Shlesinger [57] ABSTRACT A bimetallic high-speed cutting tool having aseries of spaced teeth provided on one of its longitudinal edges ismanufactured by providing each tooth at its forward top end with acut-out portion on which a tip of superhard material, molded beforebeing sintered into a shape substantially equal to a desired finalconfiguration, and having as cutting edges sharp square corners, iswelded or brazed, so that the machining of'said tip to said desiredfinal configuration, after it has been welded or brazed to the toothbody is minimized, the super-hard materials constituting said tip beingselected from those having such hardness and fiexural strength as not tobe affected by the heat applied thereto when the tip is welded or brazedfirmly onto the tooth body.

3 Claims, 3 Drawing Figures METHOD OF MANUFACTURING BIIVETALLHCHIGH-SPEED CUTTTNG TOOLS This p t on s adivision of my pndi aaprl cationSer. No. 106,681, filed Jan. 15, 1971 now U.S. Pat. No. 3,736,828.

This invention relates to a method of producing a bimetallic high-speedcutting tool which comprises forming a series of teeth with a desiredspace therebetween along one of longitudinal edges of a base made of acoil or band of flexible back-forming strip material, providing acut-out portion in each tooth having an L-shaped configuration, whenviewed in the plane of the tool, welding or brazing to the back andbottom of the cutout portion a substantially square cutting tip madefrom super-hard materials selected from alloys predominantly containingtungsten carbides, alloys of multicarbides containing as their majorportions tungsten carbides and as their minor portions titanium and/ortantalum carbides, alloys of carbides predominantly containing tantalumand/or vanadium carbides, and ceramics perdominantly containing aluminumoxides or silicon dioxides, said tip being formed, by molding or meltingthe powdery constituents of the super-hard materials to a desiredconfiguration which has a sharp cutting edge and beingbrought to finalshape and sharpness through a minor machining operation after the tiphas been welded or brazed to the tool body, the superhard materials,which form the sharp cutting tip, having a Vickers hardness of about1,300 l-lv. to 1,550 Hv. and a flexural strength of about 210 Kg./mm to160 Kg./mm so that the super-hardness proper of the materials will notadversely be affected by the temperature at which a 'welding or brazingmedium which has a Vickers hardness of about 450 l-Iv. to 500 Hv., canbe melted to form a binding surface between the tip and tooth.

Though a considerable number of experiments have been conducted and anumber of new methods have been developed for affording the edges of theteeth of a cutting blade, including a band saw blade, high heat andabrasion-resistance and consequently for giving the saw blade prolongedcutting efficiency, the saw blade made in accordance with the presentinvention is, however, based on entirely new knowledge and is producedby a method entirely different from those disclosed in the prior art.

One prior art method relating to armouring cutting edges of saw bladesis described in U.S. Pat. No. 3,104,562 which discloses a method forarmorung the edges of cutting teeth of a saw blade, in which a sphericaltip made from a super-hard alloy, such as tungsten carbide, is fittedinto a circular pocket formed at the edge of each cutting tooth and isbrazed therein. This method is almost impracticable on an industrialbasis, becuase it requires extremely elaborate technics and equipment toproduce tips of such small dimensions by molding and sintering powderyconstituents of superhard alloy, and moreover, it is nearly impossibleto economically finish the tip brazed to the edge of cutting teeth to adesired configuration.

Another method of manufacture of a high-speed cutting band saw blade, inwhich cutting teeth are formed after armouring a carbon steel backingband, is shown in U.S. Pat. No. 3,315,548. Said patent teaches a methodof manufacturing an armoured highspeed cutting saw blade, which in briefcomprises welding a wire of high-speed cutting tool steel to one edge ofa carbon steel backing band and cutting said bimetallic edge to formalong said edge teeth of the desired size and shape. This method has,however, the draw-back that only the tips of the teeth are formed ofhigh-speed cutting tool steel and the remaining greater part of saidtool steel welded to the edge is cut off from the blade, whereby theexpensive tool steel loss becomes inevitably great.

The reasons why such methods have comparatively poor productivity aredue to the fact that it is extremely difficult to mold and sinterpowdery constitutents of super-hard alloy materials into a tip ofextremely small dimensions, which correspond approximately to thedesired final configuration of the tip and its cutting edges and needlittle additional machining, and to the fact that the internal structureof a tip made from superhard alloy is adversely affected by the weldingor brazing heat, resulting in diminution of hardness and flexuralstrength to such an extent that the tip can hardly stand the high-speedcutting operation. Lowering of welding or brazing temperature so as toavoid the deterioration of the hardness and flexural strength of thetip, on the other hand, inevitably brings about lowering of the hardnessabout the welding or brazing portions to be formed between the tip andthe tooth body, resulting in said portions not being strong enough tostand the high-speed cutting operation.

In order to obtain a super-hard alloy tip having the desiredconfiguration and sharp corners, the present inventor has tried to cut,to a desired size, a material made by molding and sintering powderyconstituents of super-hard alloy, such as tungsten carbides, into stripform having a thickness corresponding to that of a saw blade, but suchtrial has ended in failure, because upon cutting the super-hard alloy ofstrip form into pieces, the sharp corners of the alloy were destroyedand it was nearly impossible to obtain, through such cutting operation,tips provided with sharp edges which can act as sharp cutting cornerswhen welded or brazed to a tool body. It should be noted, therefore,that one of the features of the present invention lies in that in orderto obtain tips of super-hard materials having closely approximate shapesor configuration which can act as sharp cutting edges when welded orbrazed to cut-out portions of blade teeth, the powdery constituents ofsuperhard alloys, which are preliminarily molded, are formed into thedesired shapes or configurations by cutting in advance of finallysintering them, and are sintered after the formation of thepreliminarily molded powdery constitutents into tips of a desired size.It should be noted also, as another feature of the present invention,that tips having comparatively small dimensions thus obtained areselected and made from such super-hard materials, to a hardness andflexural strength which is not affected by the heat to be appliedthereto when the tips are welded or brazed onto the tooth bodies.

It is, therefore, an object of the present invention to provide abimetallic high-speed cutting tool having a series of teeth provided onone of its longitudinal edges with a desired distance therebetween, thebody of each tooth being provided at its forward top end with a cutoutportion on which a tip of super-hard material, molded and sintered to ashape substantially equal to a desired final configuration and havingcutting corners, is welded or brazed so that the machining work requiredto form said tip to said desired final configuration is minimized, thesuper-hard materials constituting said tip being selected from thosehaving such hardness and flexural strength as not to be affected by theheat applied thereto in the welding or brazing of the tip to the toothbody.

In the accompanying drawing in which a preferred embodiment of thepresent invention is illustrated;

FIG. 1 is a perspective view of a part of a blade in the form of a bandsaw blade and made according to the process of the present invention;

F IG. 2 is an exploded perspective view of an enlarged scale showing atooth body having a cut-out portion with a tip of substantially squareshape; and

FIG. 3 is a plan view showing the clearance between the cut-out portionformed in a tooth body and a tip when the latter is mounted on theformer for welding or brazing thereto.

Referring now to the drawing, 4 denotes a cut-out portion formed in theforward top end of each tooth of a saw blade 1. Each cut-out portion hasa substantially L shape when viewed in the plane of the base plate 2 ofthe saw blade 1. The teeth are arranged in series with a desireddistance therebetween. A cutting tip 5 made from super-hard material,such as tungsten carbide and in the form of a substantially square blockis mounted in each cut-out portion. Each tip 5 has a back surface 6 anda bottom surface 7, by which it is welded or brazed to the cut-outportion, and is provided with a configuration and dimensionssubstantially equal to those said tip is to have after it is welded orbrazed onto the cutout portion and slightly machined along its sides. Inother words, said tip is primarily provided with such a configuration asto have sharp cutting edges wih only little additional machining. A tipmade from super-hard materials and provided with sharp corners isobtained, in the present invention, by shaping powdery constitutents ofthe material into the desired configuration before finally sintering it.In the concrete, such tips have been obtained, for example, by means ofa cold press sintering method, in which powdery constituents of alloysmixed at a specific ratio are preliminarily pressed, cut into a desiredconfiguration, and finally sintered.

Though the cutting tip 5 should preferably be provided with dimensionswhich exactly correspond to those which can act as cutting edges whenwelded or braazed to the blade, it is afforded, in practice as shown inFIG. 3 with a clearance 8 which extends transversely to the plane ofblade and has a length corresponding to about two tenths of the wholewidth, because the tip can hardly be located exactly onto the cut-outportion at its side which extends transversely to the plane of blade andnot be supported by any surfaces of the cut-out portion. It has beenfound through experiments that a welding or brazing medium, to form abinding surface between a tip 5 and its cut-out portion 4, has to beprovided with a Vickers hardness of about 450 to 500 l-Iv., to preventthe tip and the cut-out portion from separating from each other at thehighspeed cutting operation and also to insure the flexibility of theblade 1 as a whole. In order to afford the welded or brazed portion withthe aforementioned hardness, it has been found also that the welding orbrazing mediurn should be one which will solidify after heating it to atemperature of about l,300 C. It has also been found that super-hardmaterials, whose structures will not be affected by such a temperature,should have a flexural strength of about 210 I(g./mm to EXA PLE In abacking strip 2 of carbon tool steel of SK 6 containing about 0.8percent of carbon and having a thickness of 1.05 mm and a width of 32mm,there is provided along one longitudinal edge a series of teeth, eachhaving at its forward top end a cut-out portion 4 having (1) a bottomsurface of the length of 1.05 mm at its side extending transversely tothe plane of the blade, and (2) of a length of about 0.8 mm at the sideparallel to the longitudinal direction of blade, and (3) a back surfacehaving the height of about 1.5 mm. A tip made from an alloy of tungstencarbides (containing 79 percent of W, 6 percent of AiC and TaC and 15percent of Co) having a Vickers hardness of about 1,300 Hv. and aflexural strength of about 210 l(g./mm was brazed onto theaforementioned cut-out portion by first applying on the back and bottomsurfaces of the cutout portion a brazing medium predominantly containingnickel which was mixed with powdery flux and heated up to about 880 C,and subsequently mounting the tip onto the cut-out portion and heatingup to about l,300 C. Said tip was provided with a bottom surface 7 of1.3 mm at its side transverse to the plane of the blade and of 0.8 mm atits side parallel to the plane of the blade, and with a back surfacehaving a height of 1.5 mm and a top surface of 1.0 mm at its sideparallel to the plane of blade. The clearance 8' of about 0.25 mmprovided on the tip at its side extending transversely to the plane ofblade was machined after it had been brazed to the cut-out portion. TheVickers hardness of the brazed portion was measured as about 450 to 500l-Iv. It was confirmed through an experimental cutting operfation thatthe hardness and flexural strength of the tips were not affected by theaforementioned brazing temperature and the brazed portion wassufficiently strong enough to stand the cutting operation. Theexperimental cutting operation conducted with the band saw bladeobtained as described above was such that the blade mounted on a bandsawing machine was rotated at the speed of 96 m/sec. to cut a steelmaterial of 845C having the diameter of 200 mm. The cutting depth ofeach tooth into the material was about 0.2 mm and the material was cutin about seconds.

E AM LE .2-

A band saw blade having a structure and construction the same as thosedescribed in the foregoing Example 1 and produced in a similar mannerbut provided with tips made from an alloy steel containing 82 percent ofW, 10 percent TaC and AiC and 8 percent of Co and having a Vickershardness of about 1,550 l(g./mm has also shown extremely good cuttingefficiency.

Having thus described my invention, what I claim is:

l. A method of producing a bimetallic high-speed cutting tool, whichcomprises forming on a base strip of flexible material a series of teethwhich are spaced from one another along one of the longitudinal edges ofsaid strip,

providing a cut-out portion in each tooth that has an L-shapedconfiguration, when viewed in the longitudinal plane of the tooth,

compacting a powdery super-hard material to a shape conformingapproximately to the cut-out portion of each tooth, cutting thecompacted material to the desired configuration, and then sintering thecompacted material to form a cutting tip of generally truncatedpyramidal shape,

applying a brazing medium to the back and bottom portions of the cut-outportion of each tooth,

heating the brazing medium,

mounting a cutting tip on the cut-out portion of each tooth so that thebottom of the tip seats on the braze-coated bottom of said cut-outportion and the back of the tip seats against the braze-coated back ofthe cut-out portion,

then heating the brazing medium to a higher temperature than the initialheat but below the melting temperature of the tip to braze the tip tothe tooth on which it is seated, and

then machining each tip to provide sharp cutting edges thereon.

2. A method of producing a high speed cutting tool as claimed in claim1, wherein the tips are initially molded to be slightly wider than thecut-out portions of the flexible base strip, and machining each tip,after it has been brazed to the associated cut-out portion to conform itprecisely to the desired configuration.

3. A method of producing a high-speed cutting tool as claimed in claim2, wherein the tips have a Vickers hardness of about 1,300 Hv. to 1,550Hv. and a flexural strength of about 210 Kg./mm to Kglmrn the brazingmedium has a Vickers hardness of about 450 Hv. to 500 Hv., and thebrazing medium is initially heated figJtGaBOut 800C., and the brazing iseffected at about 1,300C.

1. A method of producing a bimetallic high-speed cutting tool, whichcomprises forming on a base strip of flexible material a series of teethwhich are spaced from one another along one of the longitudinal edges ofsaid strip, providing a cut-out portion in each tooth that has anL-shaped configuration, when viewed in the longitudinal plane of thetooth, compacting a powdery super-hard material to a shape conformingapproximately to the cut-out portion of each tooth, cutting thecompacted material to the desired configuration, and then sintering thecompacted material to form a cutting tip of generally truncatedpyramidal shape, applying a brazing medium to the back and bottomportions of the cut-out portion of each tooth, heating the brazingmedium, mounting a cutting tip on the cut-out portion of each tooth sothat the bottom of the tip seats on the braze-coated bottom of saidcut-out portion and the back of the tip seats against the braze-coatedback of the cut-out portion, then heating the brazing medium to a highertemperature than the initial heat but below the melting temperature ofthe tip to braze the tip to the tooth on which it is seated, and thenmachining each tip to provide sharp cutting edges thereon.
 2. A methodof producing a high speed cutting tool as claimed in claim 1, whereinthe tips are initially molded to be slightly wider than the cut-outportions of the flexible base strip, and machining each tip, after ithas been brazed to the associated cut-out portion to conform itprecisely to the desired configuration.
 3. A method of producing ahigh-speed cutting tool as claimed in claim 2, wherein the tips have aVickers hardness of about 1,300 Hv. to 1,500 Hv. and a flexural strengthof about 210 Kg./mm2 to 160 Kg/mm2, the brazing medium has a Vickershardness of about 450 Hv. to 500 Hv., and the brazing medium isinitially heated up to about 800* C., and the brazing is effected atabout 1,300* C.